Android插件化（一）：使用改进的MultiDex动态加载assets中的apk_调用安装assets 内apk

Android插件化（一）：使用改进的MultiDex动态加载assets中的apk

简介

为了解决65535方法数超标的问题，Google推荐使用MultiDex来加载classes2.dex,classes3.dex等等，其基本思想就是在运行时动态修改ClassLoader，以达到动态加载类的目的。为了更好的理解MultiDex的工作原理，可以先看一下ClassLoader的工作原理[1].然后参见PathClassLoader的源码，当然，它继承自BaseDexClassLoader，主要源码都在BaseDexClassLoader中。MultiDex加载离线apk的过程如下：

我们可以在Application的onCreate方法或者Activity的attachBaseContext方法中开发加载。

动态加载assets中的apk

根据MultiDex的源码，我们可以修改其install方法，然后从assets资源中解压出所需要加载的apk文件，然后调用installSecondaryDexes方法，将其加载到当前Application的ClassLoader当中，这样，在运行的时候，就可以通过当前的ClassLoader查找到离线apk中的类了。

[AssetsMultiDexLoader.class]

package net.mobctrl.hostapk;

import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.ListIterator;
import java.util.Set;
import java.util.zip.ZipFile;

import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Build;
import android.util.Log;
import dalvik.system.DexFile;

/**
 * @Author Zheng Haibo
 * @Mail mochuan.zhb@alibaba-inc.com
 * @Company Alibaba Group
 * @PersonalWebsite http://www.mobctrl.net
 * @version $Id: AssetsDex.java, v 0.1 2015年12月10日 下午5:36:23 mochuan.zhb Exp $
 * @Description ClassLoader
 */
public class AssetsMultiDexLoader {
   

    private static final String TAG = "AssetsApkLoader";

    private static boolean installed = false;

    private static final int MAX_SUPPORTED_SDK_VERSION = 20;

    private static final int MIN_SDK_VERSION = 4;

    private static final Set<String> installedApk = new HashSet<String>();

    private AssetsMultiDexLoader() {

    }

    /**
     * 安装Assets中的apk文件
     * 
     * @param context
     */
    public static void install(Context context) {
        Log.i(TAG, "install...");
        if (installed) {
            return;
        }
        try {
            clearOldDexDir(context);
        } catch (Throwable t) {
            Log.w(TAG,
                    "Something went wrong when trying to clear old MultiDex extraction, "
                            + "continuing without cleaning.", t);
        }
        AssetsManager.copyAllAssetsApk(context);
        Log.i(TAG, "install");
        if (Build.VERSION.SDK_INT < MIN_SDK_VERSION) {
            throw new RuntimeException("Multi dex installation failed. SDK "
                    + Build.VERSION.SDK_INT
                    + " is unsupported. Min SDK version is " + MIN_SDK_VERSION
                    + ".");
        }
        try {
            ApplicationInfo applicationInfo = getApplicationInfo(context);
            if (applicationInfo == null) {
                // Looks like running on a test Context, so just return without
                // patching.
                return;
            }
            synchronized (installedApk) {
                String apkPath = applicationInfo.sourceDir;
                if (installedApk.contains(apkPath)) {
                    return;
                }
                installedApk.add(apkPath);
                if (Build.VERSION.SDK_INT > MAX_SUPPORTED_SDK_VERSION) {
                    Log.w(TAG,
                            "MultiDex is not guaranteed to work in SDK version "
                                    + Build.VERSION.SDK_INT
                                    + ": SDK version higher than "
                                    + MAX_SUPPORTED_SDK_VERSION
                                    + " should be backed by "
                                    + "runtime with built-in multidex capabilty but it's not the "
                                    + "case here: java.vm.version=\""
                                    + System.getProperty("java.vm.version")
                                    + "\"");
                }
                /*
                 * The patched class loader is expected to be a descendant of
                 * dalvik.system.BaseDexClassLoader. We modify its
                 * dalvik.system.DexPathList pathList field to append additional
                 * DEX file entries.
                 */
                ClassLoader loader;
                t
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